2. The glass composition of claim 1, having an oxidization property in a
molten state.

3. The glass composition of claim 1, containing 1.1 wt % or more MoO3
in terms of oxides.

4. The glass composition of claim 2, containing 1.1 wt % or more MoO3
in terms of oxides.

5. The glass composition of claim 1, whereina thermal expansion
coefficient α30/380 is in a range of 34.times.10.sup.-7/K to
43.times.10.sup.-7/K inclusive.

6. The glass composition of claim 4, whereina thermal expansion
coefficient α30/380 is in a range of 34.times.10.sup.-7/K to
43.times.10.sup.-7/K inclusive.

7. The glass composition of claim 1, whereina thermal expansion
coefficient α30/380 is in a range of 43.times.10.sup.-7/K to
55.times.10.sup.-7/K inclusive.

8. The glass composition of claim 4, whereina thermal expansion
coefficient α30/380 is in a range of 43.times.10.sup.-7/K to
55.times.10.sup.-7/K inclusive.

9. A lamp including a glass bulb that is made of the glass composition of
claim 1.

10. A lamp including a glass bulb that is made of the glass composition of
claim 3.

11. A backlight unit on which the lamp of claim 9 is disposed.

12. A backlight unit comprising:a plurality of lamps of claim 10; anda
diffusion plate made from a polycarbonate resin disposed on a
light-emission side of the plurality of lamps.

13. A method for producing a glass composition for lamps comprising:a
mixing step of mixing glass materials so that the glass composition
substantially contains the following that are expressed in terms of
oxides:SiO2: 55 to 75 wt %;B2O3: 11 to 25 wt %;MoO3:
0.3 to 1.4 wt %;Al2O3: 1 to 10 wt %;Li2O: 0 to 10 wt
%;Na2O: 0 to 10 wt %;K2O: 0 to 10 wt
%;Li2O+Na2O+K2O: 1 to 10 wt %;MgO: 0 to 5 wt %;CaO: 0 to
10 wt %;SrO: 0 to 10 wt %;BaO: 0 to 10 wt %; andMgO+CaO+SrO+BaO: 1 to 10
wt %; anda melting step of melting the mixed glass materials to make the
glass composition in a molten state, whereinthe glass materials in the
molten state are oxidized in the melting step.

14. The method of claim 13, whereina part of the glass materials mixed in
the mixing step is alkali metal nitrate, andthe glass materials in the
molten state are oxidized in the melting step by melting the alkali metal
nitrate.

15. The method of claim 13, whereinthe alkali metal nitrate is either
NaNO3 or KNO3, or both NaNO3 and KNO.sub.3.

16. The method of claim 14, whereinthe alkali metal nitrate is either
NaNO3 or KNO3, or both NaNO3 and KNO.sub.3.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a glass composition for lamps, a
lamp, a backlight unit, and a method for producing the glass composition
for lamps.

BACKGROUND ART

[0002]For a backlight such as a liquid crystal display device, a lamp is
used as a light source. In order to reduce a thickness and a weight of a
backlight, it is preferable that a glass bulb of the lamp is formed so as
to have a small diameter and a thin wall. Therefore, the glass bulb is
generally formed by borosilicate acid glass.

[0003]The borosilicate acid glass is better in heat resistance than
soda-lime glass because the borosilicate acid glass has a higher
softening point, a higher anneal temperature, and a small coefficient of
thermal expansion. Therefore, the glass bulb hardly suffers from thermal
deformation under a high temperature condition in a phosphor film
calcination process, even if being formed so as to have a small diameter
and a thin wall. Also, the borosilicate acid glass is better in
mechanical strength because the borosilicate acid glass has a higher
Young's modulus and a higher Vickers hardness. Therefore, the glass bulb
is hardly broken even if being formed so as to have a small diameter and
a thin wall.

[0004]Note that borosilicate acid glass in the present invention means
glass containing 11 wt % or more B2O3 in terms of the oxides.

[0005]By the way, glass for lamps is required to have an ultra violet
shielding effect and an anti-solarization effect. The ultra violet
shielding effect suppresses that an ultra violet ray generated in a lamp
transmits to an outside of the lamp, and the anti-solarization effect
suppresses coloring of glass caused by an ultra violet ray
(solarization). On the other hand, in Patent Documents 1, 2, and 3, the
following borosilicate acid glass is disclosed. The ultra violet
shielding effect and the anti-solarization effect are given to the
borosilicate acid glass by adding an ultra violet shielding agent such as
TiO2.

[0006]However, if adding an ultra violet shielding agent such as TiO2
to borosilicate acid glass, a lamp luminous flux decreases because glass
is colored and visible light is shielded. On the other hand, if
decreasing an additive amount of an ultra violet shielding agent to
prevent glass from being colored, the ultra violet shielding effect
becomes insufficient.

[0007]The present invention aims to provide a glass composition for lamps
that has a high ultra violet shielding effect and hardly suffers from
coloring, and a method for producing the glass composition. Also, the
present invention further aims to provide a lamp that is high in lamp
luminous flux.

[0009]In accordance with an aspect of the glass composition for lamps of
the present invention, the glass composition has an oxidization property
in a molten state.

[0010]In accordance with another aspect of the glass composition for lamps
of the present invention, the glass composition contains 1.1 wt % or more
MoO3 in terms of oxides.

[0011]In accordance with another aspect of the glass composition for lamps
of the present invention, a thermal expansion coefficient
α30/380 is in a range of 34×10-7/K to
43×10-7/K inclusive.

[0012]In accordance with another aspect of the glass composition for lamps
of the present invention, a thermal expansion coefficient
α30/380 is in a range of 43×10-7/K to
55×10-7/K inclusive.

[0013]The lamp of the present invention includes a glass bulb that is made
of the above-mentioned glass composition.

[0014]The above-mentioned lamp is disposed on the backlight unit of the
present invention.

[0015]In accordance with an aspect of the backlight unit of the present
invention, the backlight unit comprises a plurality of the
above-mentioned lamps, and a diffusion plate made from a polycarbonate
resin disposed on a light-emission side of the plurality of lamps.

[0016]The method for producing the glass composition for lamps of the
present invention comprises a mixing step of mixing glass materials so
that the glass composition substantially contains the following that are
expressed in terms of oxides: SiO2: 55 to 75 wt %; B2O3:
11 to 25 wt %; MoO3: 0.3 to 1.4 wt %; Al2O3: 1 to 10 wt %;
Li2O: 0 to 10 wt %; Na2O: 0 to 10 wt %; K2O: 0 to 10 wt %;
Li2O+Na2O+K2O: 1 to 10 wt %; MgO: 0 to 5 wt %; CaO: 0 to
10 wt %; SrO: 0 to 10 wt %; BaO: 0 to 10 wt %; and MgO+CaO+SrO+BaO: 1 to
10 wt %; and a melting step of melting the mixed glass materials to make
the glass composition in a molten state, wherein the glass materials in
the molten state are oxidized in the melting step.

[0017]In accordance with an aspect of the method for producing the glass
composition for lamps of the present invention, a part of the glass
materials mixed in the mixing step is alkali metal nitrate, and the glass
materials in the molten state are oxidized in the melting step by melting
the alkali metal nitrate.

[0018]In accordance with another aspect of the method for producing the
glass composition for lamps of the present invention, the alkali metal
nitrate is either NaNO3 or KNO3, or both NaNO3 and
KNO3.

EFFECTS OF THE INVENTION

[0019]MoO3 in the range of 0.3 to 1.4 wt %, in terms of the oxides,
is added to the glass composition for lamps of the present invention, and
the cation percentage of Mo6+ and Mo.sup.Other of the Mo ions in the
glass composition satisfies the relation of:
(Mo6+)/[(Mo6+)+(Mo.sup.Other)]≧0.8. Therefore, the glass
composition has a sufficient ultra violet shielding effect and a
sufficient anti-solarization effect, and coloring is less likely to
occur.

[0020]After having conducted various investigations, the inventors of the
present invention ascertained that Mo6+ does not cause coloring of
glass, but Mo.sup.Other causes coloring of glass. Also, the inventors
found out that if Mo.sup.Other is small in amount, coloring is less
likely to occur, and especially if the cation percentage of Mo6+ and
Mo.sup.Other satisfies the above-mentioned relation, it is highly
unlikely that coloring of glass occurs.

[0021]If the glass composition for lamps of the present invention is
oxidized in a molten state, Mo.sup.Other is small in amount, and coloring
is less likely to occur.

[0022]Also, if the glass composition for lamps of the present invention
contains 1.1 wt % or more MoO3, in terms of the oxides, the
following effects can be obtained.

[0023]Generally, diffusion plates made from an acrylic resin are used for
backlight units for liquid crystal TVs. However, the diffusion plates are
easily warped by absorbing moisture, causing an error of measurements as
they get larger. Therefore, diffusion plates made from a PC
(polycarbonate) resin which warp less are used for backlight units for
large liquid crystal display TVs with the size of the displays larger
than 17 inches.

[0024]The diffusion plates made from the PC resin, however, are discolored
and deteriorated by a 313 nm ultra violet ray severely, compared to the
diffusion plates made from the acrylic resin. A conventional glass for
lamps can sufficiently shield a 186 nm and a 254 nm ultra violet ray out
of ultra violet rays emitted from mercury, but cannot shield a 313 nm
ultra violet ray sufficiently. Therefore, because of a 313 nm ultra
violet ray transmitted and leaked from a lamp, diffusion plates and
diffusion sheets made from the PC resin are discolored and deteriorated,
deteriorating the luminance of backlight units.

[0025]Therefore, an idea of adding WO3 and TiO2, for example, to
the glass to suppress the transmission of a 313 nm ultra violet ray can
be considered. However, since WO3 and TiO2 have a property of
increasing crystallization of the glass, the glass can cause a
devitrification (a phenomenon of losing transparency) in melting or in a
heating process during lamp production.

[0026]On the other hand, when 1.1 wt % or more MoO3, in terms of the
oxides, is added to the glass composition of the present invention, it is
possible to suppress the transmission of a 313 nm ultra violet ray
sufficiently with small discoloration/deterioration of resin components.
In addition, the resin components have no devitrification and
substantially no coloring.

[0027]The glass composition for lamps of the present invention achieves
the following effects when the coefficient of thermal expansion
(α30/380) is 34×10-7/K to 43×10-7/K or
43×10-7/K to 55×10-7/K.

[0028]Generally, a lead wire made of tungsten or kovar alloy, which is
capable of resisting the heat caused by a discharge, is used for a lamp
for a backlight. Consequently, it is preferable to bring the coefficient
of thermal expansion of glass close to that of tungsten and kovar alloy,
in order to increase the reliability of airtight sealing of the lead
wire.

[0029]In the case of the coefficient of thermal expansion
(α30/380) of the glass composition being 34×10-7/K
to 43×10-7/K, the coefficient of thermal expansion of the
glass composition is same as that of the lead wire made of tungsten.
Therefore, owing to the high chemical resistance, the reliability of
airtight sealing of the lead wire is high.

[0030]When the coefficient of thermal expansion (α30/380) of
the glass composition is 43×10-7/K to 55×10-7/K,
the coefficient of thermal expansion of the glass composition is same as
that of the lead wire made of kovar alloy. Therefore, owing to the high
chemical resistance, the reliability of airtight sealing of the lead wire
is high.

[0031]The lamp of the present invention includes a glass bulb made of the
above glass composition. Therefore, the glass of the glass bulb has
little coloring and a visible light transmittance is high so that the
lamp luminous flux is high.

[0032]Since the backlight unit of the present invention is provided with
the above lamp with high lamp luminous flux, the luminance is high.

[0033]Also, when the lamp including the glass bulb made of the glass
composition to which 1.1 wt % or more MoO3 is added is provided with
the backlight unit of the present invention, the deterioration and
discoloration of a diffusion plate 14 and a diffusion sheet 15 caused by
a 313 nm ultra violet ray are effectively suppressed. Consequently, the
decrease in the surface luminance caused by the use of a backlight unit
is suppressed remarkably, so that a backlight unit 10 has a long life.

[0034]A high-vision technology for liquid crystal display TVs has been
evolving in recent years. High-vision liquid crystal display TVs have a
smaller opening ratio and require a higher surface luminance than normal
liquid crystal display TVs. Therefore, the surface luminance of a
backlight unit has been boosted by increasing the number of cold cathode
fluorescent lamps, for example. Raising the surface luminance of the
backlight unit in this way leads to an increase in the amount of a 313 nm
ultra violet ray, which severely deteriorates and discolors the diffusion
and reflection plates, and conversely causes a drop in the surface
luminance of the backlight unit. However, such drop in the surface
luminance of the backlight unit of the present invention hardly occurs.

[0035]Furthermore, there have been increasing demands in recent years for
longer life liquid crystal display TVs, an example of which is the call
for liquid crystal display TVs having an operating time in excess of
60,000 hours. Since the decrease in the surface luminance of the
backlight unit of the present invention hardly occurs, it is possible to
extend the life of the liquid crystal display TVs.

[0036]Also, when the glass composition constituting the glass bulb
contains 1.1 wt % or more MoO3, in terms of the oxides, the
transmission of a 313 nm ultra violet ray generated by mercury can be
suppressed sufficiently. Therefore, even if the glass composition is used
for a backlight unit, the discoloration and deterioration of resin
components are little and the reliability of the backlights is high.

[0037]According to the method for producing the glass composition for
lamps of the present invention, the glass composition in a molten state
is oxidized in a melting process. Therefore, it is possible to suppress
coloring of the above glass composition more effectively. In other words,
if the glass composition in the molten state is oxidized in the melting
process, a valence change of Mo ion (herein after, referred to as
"valence change") such as a case in which Mo6+ is deoxidized to
Mo.sup.Other can be efficiently suppressed. As a result, Mo.sup.Other is
small in amount and the glass has little coloring.

[0038]Especially, if the glass composition in the molten state is oxidized
by using alkali metal nitrate for a part of a glass material, the glass
composition for lamps of the present invention can be produced by the
same production process as the conventional technology, without adding
new processes.

[0039]Moreover, if either NaNO3 or KNO3, or both NaNO3 and
KNO3 are used as the alkali metal nitrate, the glass composition can
be produced at relatively low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1 shows a composition and a property of a glass composition of
an embodiment of the present invention.

[0041]FIG. 2 is a schematic view showing an essential structure of a cold
cathode fluorescent lamp of an embodiment of the present invention.

[0042]FIG. 3 is a schematic view showing an essential structure of a
backlight unit of an embodiment of the present invention.

[0047]A glass composition for lamps, a lamp, a backlight unit, and a
method for producing the glass composition for lamps are described with
reference to the accompanying drawings.

<Description of the Glass Composition for Lamps>

[0048]The constituents of the glass composition of the present invention,
in terms of oxides, are shown in No. 1 to 5 in FIG. 1.

[0049]Here, the constituents of the glass composition of the present
invention are not limited to the constituents shown in No. 1 to 5.
However, in order to maintain a property as glass for lamps, it is
preferable that the glass composition of the present invention consists
substantially of the following constituents expressed in terms of oxides:
SiO2: 55 to 75 wt %, B2O3: 11 to 25 wt %, MoO3: 0.3
to 1.4 wt %, Al2O3: 1 to 10 wt %, Li2O: 0 to 10 wt %,
Na2O: 0 to 10 wt %, K2O: 0 to 10 wt %,
Li2O+Na2O+K2O: 1 to 10 wt %, MgO: 0 to 5 wt %, CaO: 0 to
10 wt %, SrO: 0 to 10 wt %, BaO: 0 to 10 wt %, MgO+CaO+SrO+BaO: 1 to 10
wt %.

[0050]SiO2 is a main component for forming a mesh structure of the
glass, and a content thereof is in a range of 55 to 75 wt % inclusive.
When SiO2 is less than 55 wt %, the chemical resistance of the glass
becomes insufficient, and the coefficient of thermal expansion becomes
too large. As a result, airtight sealing of the lead wire becomes
difficult. On the other hand, when SiO2 is more than 75 wt %, the
glass viscosity becomes too high, making melting and forming of the glass
difficult. Moreover, the coefficient of thermal expansion becomes too
small, making airtight sealing of the lead wire difficult.

[0051]B2O3 is a component for forming a mesh structure of the
glass, and a content thereof is in a range of 11 to 25 wt % inclusive. If
B2O3 is added, a glass easy-to-melt property and the chemical
resistance can be improved, and the coefficient of thermal expansion
becomes small. When B2O3 is less than 11 wt %, the chemical
resistance becomes insufficient, along with deteriorating the glass
easy-to-melt property. Also, the coefficient of thermal expansion becomes
too large, making airtight sealing of the lead wire difficult. On the
other hand, when B2O3 is more than 25 wt %, an evaporation
amount of a glass component increases in a melting process, and it is
difficult to obtain uniform glass. Moreover, the coefficient of thermal
expansion becomes too small, making airtight sealing of the lead wire
difficult.

[0052]MoO3 is an essential component of the glass composition of the
present invention, and gives the glass a high ultra violet shielding
effect and a high anti-solarization effect. When 0.3 wt % or more
MoO3 is added, a 186 nm and a 254 nm ultra violet rays can be
sufficiently shielded. Especially when 1.1 wt % or more MoO3 is
added, even a 313 nm ultra violet ray can be sufficiently shielded.

[0053]Note that Mo ion gives the glass the ultra violet shielding effect
and the anti-solarization effect even if Mo ion is contained in each
state of Mo ion from divalent Mo ion to hexavalent Mo ion. However, the
glass does not cause coloring because of Mo6+. Regarding the glass
composition of the present invention, melted glass is oxidized when
melting a glass material. Therefore, a valence change of Mo ion in the
melted glass is suppressed, and a state of Mo6+ is maintained.

[0054]When MoO3 is less than 0.3 wt %, the ultra violet shielding
effect becomes insufficient. On the other hand, when MoO3 is more
than 1.4 wt %, the glass is likely to be colored to brown. This is
because if an amount Moother ion increases along with an increase of
a whole amount of Mo ion, it becomes difficult to suppress coloring only
by suppressing a valence change of Mo ion.

[0055]Al2O3 is a component for forming a mesh structure of the
glass, and a content thereof is in a range of 1 to 10 wt % inclusive. If
Al2O3 is added, the chemical resistance of the glass can be
improved. When Al2O3 is less than 1 wt %, the chemical
resistance becomes insufficient. On the other hand, when Al2O3
is more than 10 wt %, the glass viscosity becomes too high, making
melting and forming of the glass difficult. Moreover, the coefficient of
thermal expansion becomes too large, making airtight sealing of the lead
wire difficult.

[0056]Na2O, K2O, and Li2O which are alkaline metal oxides
are components for giving a function to a mash structure of the glass.
When these alkaline metal oxides are added, the viscosity of the glass
decreases, making melting and forming of glass easy. Also, the
coefficient of thermal expansion of the glass becomes large.

[0057]A content of Li2O is in a range of 0 to 5 wt % inclusive, a
content of Na2O is in a range of 0 to 8 wt % inclusive, and a
content of K2O is in a range of 0 to 12 wt % inclusive. The total
content of Na2O, K2O, and Li2O is in a range of 1 to 10 wt
% inclusive. When the total content is less than 1 wt %, the viscosity of
the glass becomes too high, making melting and forming of the glass
difficult. On the other hand, when the total content is more than 10 wt
%, alkaline metal ion is eluted from the glass to a glass surface,
resulting in the decrease in chemical resistance. Moreover, the
coefficient of thermal expansion becomes too large, making airtight
sealing of the lead wire difficult.

[0058]In order to maintain a valence of Mo ion in the glass at Mo6+,
a part of the alkaline metal oxides is added in a form of nitrate as an
oxidant. It is preferable that an additive amount of alkaline metal
nitrate as an oxidant is equal to or larger than 0.5 times as large as an
additive amount of MoO3 in weight percentage.

[0059]MgO, CaO, SrO, and BaO which are alkaline earth metal oxides are
components forgiving a function to a mash structure of the glass. If
these alkaline earth metal oxides are added, the viscosity of the glass
decreases, making melting and forming of the glass easy. Also, the
coefficient of thermal expansion of the glass becomes large.

[0060]A content of MgO is in a range of 0 to 5 wt % inclusive, a content
of CaO is in a range of 0 to 10 wt % inclusive, a content of SrO is in a
range of 0 to 10 wt % inclusive, and a content of BaO is in a range of 0
to 10 wt % inclusive. The total content of MgO, CaO, SrO, and BaO is in a
range of 1 to 10 wt % inclusive. When the total content is less than 1 wt
%, the viscosity of the glass becomes too high, making melting and
forming of the glass difficult. Also, a chemical resistance of the glass
decreases. On the other hand, when the total content is more than 10 wt
%, the coefficient of thermal expansion becomes too large, making
airtight sealing of the lead wire difficult.

[0061]Here, the glass composition of present invention may include a metal
oxide other than those described above as long as the contents of each
component are substantially within the above described range and the
scope of the above constituents. Examples of a metal oxide include
Sb2O3, ZnO, ZrO, P2O5, TiO2, PbO,
As2O3 and the like.

[0062]Note that TiO2 increases the crystalline of the glass, causing
a devitrification. Therefore, it is preferable that TiO2 is not
contained except for a case in which TiO2 is mixed as impurities of
a glass material. Also, PbO and As2O3 are materials which add a
load to an environment, and increase a material cost because of a high
cost. Therefore, it is preferable that PbO and As2O3 are not
contained except for a case in which PbO and As2O3 are mixed as
impurities of a glass material.

<Description of the Method for Producing the Glass Composition for
Lamps>

[0063]The method for producing the glass composition of the present
invention is described in the following.

[0064]Firstly, in a mixing process, a plurality of types of glass
materials are mixed so that the glass after melting is within the range
of the glass composition of the present invention. Next, in a melting
process, the mixed glass materials are thrown into a glass melting
furnace, and melted at a temperature in a range of 1500° C. to
1600° C. inclusive for vitrification, in order to obtain glass
melting liquid.

[0065]In the mixing process, alkali metal nitrate is mixed as a part of
the glass materials. Since alkali metal nitrate serves as an oxidant in
the glass melting liquid in the melting process, the glass melting liquid
become oxidized, and the valence change of Mo is suppressed. As alkali
metal nitrate, NaNO3 and KNO3 can be used. Either NaNO3 or
KNO3, or both NaNO3 and KNO3 can be used.

[0066]Note that the method of oxidizing the glass melting liquid is not
limited to the method of using alkali metal nitrate, and the glass
melting liquid may be oxidized by adding other compound as an oxidant.
Also, alkali metal nitrate is not limited to NaNO3 and KNO3,
and other alkali metal nitrate may be used.

[0067]It is preferable that an additive amount of an oxidant such as
alkali metal nitrate is equal to or larger than 0.5 times as large as an
additive amount of MoO3, in weight percentage. If the additive
amount of the oxidant is less than 0.5 times as large as the additive
amount of MoO3, there is a possibility that the glass melting liquid
is not sufficiently oxidized, and the valence change of Mo ion cannot be
sufficiently suppressed.

[0068]After the melting process, the melting glass liquid is formed into a
tube using a tube drawing method such as a Danner method and the like,
and then cut into a tube having the predetermined size to manufacture a
glass tube for lamps. In addition, the glass tube is heat-processed to
manufacture a glass bulb. Then various types of lamps are manufactured.

[0069]In the present invention, the following are defined as the glass
composition in the molten state. One is glass melting liquid which is
formed from the glass material melted in the furnace, and the other is
the glass composition in the molten state which has been cooled once to
be the glass composition and then has been melted again by heating.

(About Lamps)

[0070]A straight tube-shaped cold cathode fluorescent lamp is described as
one embodiment of the lamp of the present invention with reference to the
accompanying drawings. FIG. 2 is the schematic view showing the essential
structure of a cold cathode fluorescent lamp 1 of one embodiment of the
present invention. The structure of the cold cathode fluorescent lamp 1
basically corresponds to that of a conventional cold cathode fluorescent
lamp.

[0071]A glass bulb 2 of the cold cathode fluorescent lamp 1 is made of the
above glass composition, and its outer diameter, inner diameter and total
length are approximately 4.0 mm, approximately 3.4 mm and approximately
730 mm respectively. The glass bulb 2 is manufactured by taking the
following steps. Firstly, materials that are mixed to be predetermined
constituents are thrown to the glass melting furnace and melted at a
temperature in a range of 1500° C. to 1600° C. inclusive
for vitrification. Then, the resultant glass melting liquid is formed
into a tube by using the tube drawing method such as a Danner method and
the like. After that, the tube is cut into the predetermined size and
heat-processed to obtain a glass tube. By using the glass tube, it is
possible to manufacture various types of lamps in the usual manner.

[0072]Here, the outer and inner diameters and the total length of the
glass bulb 2 are not limited to the above. However, since the glass bulb
2 for the cold cathode fluorescent lamp 1 is desired to have the small
tube diameter and thin wall thickness, the preferable outer diameter of
the glass bulb 2 is in the range of 1.8 mm to 6.0 mm inclusive, and the
preferable inner diameter of that is in the range of 1.4 mm to 5.0 mm
inclusive.

[0073]The glass bulb 2 is sealed airtight at each end by a piece of a bead
glass 3. In a vicinity of each end of the glass bulb 2, a lead wire 4
made of tungsten or kovar alloy and having an approximately 0.8 mm
diameter is sealed airtight, so as to pass through the bead glass 3.
Furthermore, a cap-shaped electrode 5 is attached to each lead wire 4 at
the end disposed within the glass bulb 2. Here, the electrode 5 is made
from nickel or niobium and its surface is coated with an electron
radioactive material. Note that the pieces of the bead glass 3, the lead
wire 4 and the electrode 5 are not limited to the above structure.

[0074]A rare earth phosphor 6 formed from a mixture of red, green, and
blue phosphors (Y2O3: Eu, LaO4: Ce, Tb,
BaMg2Al16O27: Eu, Mn) are applied to the inner surface of
the glass bulb 2. Also, mercury in a range of 0.8 mg to 2.5 mg inclusive
(not illustrated) and a rare gas such as xenon and the like (not
illustrated) are enclosed within the glass bulb 2.

[0075]Up to now, although the cold cathode fluorescent lamp of the present
invention is described specifically with reference to the embodiment, the
content of the present invention is not limited to the above embodiment.

(Description of Backlight Unit)

[0076]FIG. 3 is the schematic view showing the essential structure of a
direct-type backlight unit of one embodiment of the present invention.
The structure of a direct-type backlight unit 10 of the embodiment of the
present invention basically corresponds to that of a conventional
backlight unit.

[0077]An enclosure 11 made from a white PET (polyethylene terephthalate)
resin is formed from a substantially rectangular reflection plate 12 and
a plurality of side plates 13 disposed so as to surround the reflection
plate 12. A plurality of evenly spaced cold cathode fluorescent lamps 1
are housed in a horizontal lighting direction within the enclosure 11, so
as to be close to the reflection plate 12.

[0078]The diffusion plate 14 made from a PC resin is disposed in the
enclosure 11, so as to be in opposition to the reflection plate 12 with
the cold cathode fluorescent lamps 1 there between. In the backlight unit
10, the side on which the diffusion plate 14 is disposed relative to the
cold cathode fluorescent lamps 1 is the light-emission side of the
backlight unit 10, while the side on which the reflection plate 12 is
disposed relative to the cold cathode fluorescent lamps 1 is the
light-reflecting side of the backlight unit 10. The diffusion sheet 15
made from the PC resin and a lens sheet 16 made from the acrylic resin
are disposed on the light-emission side of the diffusion plate 14 so as
to overlap one another.

[0079]With a liquid crystal display TV that employs the backlight unit 10,
a liquid crystal display panel 17 of the liquid crystal display TV is
disposed on the light-emission side of the lens sheet 16.

[0080]Note that the backlight unit 10 is not limited to the above
structure. Consider a typical configuration in which the backlight unit
10 is used in a 32-inch liquid crystal display TV, for example. In this
case, the measurements of the enclosure 11 are set to a width of
approximately 408 mm, a length of approximately 728 mm, and a depth of
approximately 19 mm. Also, sixteen cold cathode fluorescent lamps 1 are
disposed in the enclosure 11 at equally spaced intervals of approximately
25.7 mm. Also, the total length of the cold cathode fluorescent lamp 1 is
approximately 730 mm and the outer and inner diameters of the glass bulb
2 are set to approximately 4.0 mm and approximately 3.4 mm respectively.
When such backlight unit 10 is operated at a 5.5 mA lamp power, a surface
luminance of approximately 8000 cd/m2 is obtained with the lens
sheet 16.

(Description of Experiment)

[0081]Through experiment, the inventors investigated an additive amount of
MoO3 and an additive amount of an oxidant which are required for
obtaining a glass composition having a high ultra violet shielding
effect, a high anti-solarization effect, and less coloring.

[0082]In the experiment, the glass of each constituent shown in FIG. 1 was
manufactured to evaluate glass characteristics. Each glass was
manufactured by taking the following steps. Respective glass materials
were mixed to have the same constituents as shown in FIG. 1, and put in a
platinum crucible. The mixture was heat-melted in an electric furnace at
a temperature of 1500° C. for 3 hours. Then, the resultant mixture
was sufficiently clarified and poured onto a carbon mold to form in a
plate shape or board shape, and cooled in the electric furnace.

[0083]As for an ultra violet transmittance, a glass sample was
manufactured by polishing both sides of a plate-shaped glass having a
diameter of 20 mm and a thickness of 2 mm so as to be mirror surfaces.
Then, a transmittance of a 254 nm ultra violet ray of the glass sample
(T254), and a transmittance of a 313 nm ultra violet ray of the
glass sample (T313) were measured by a spectrophotometer. Note that
the ultra violet transmittance means a transmittance at a plate thickness
of 2 mm.

[0084]The ultra violet shielding effect was evaluated based on T254
and T313. More specifically, when T254 was less than 1.0% and
T313 was less than 5.0%, the ultra violet shielding effect was
judged to be ".circleincircle.". When T254 was less than 1.0% and
T313 was equal to or more than 5.0%, the ultra violet shielding
effect was judged to be "◯". On the other hand, when
T254 was equal to or more than 1.0%, the ultra violet shielding
effect was judged to be "X". When the judgment was "◯" and
".circleincircle.", the ultra violet shielding effect was evaluated to be
high.

[0085]As for the visible light transmittance, a glass sample was
manufactured by polishing both sides of a plate-shaped glass having a
diameter of 20 mm and a thickness of 2 mm so as to be mirror surfaces.
Then, a transmittance of 400 nm visible light of the glass sample
(T400), and a transmittance of 550 nm visible light of the glass
sample (T550) were measured by a spectrophotometer. Note that the
visible light transmittance means a transmittance at a plate thickness of
2 mm.

[0086]Coloring was evaluated based on T400 and T550. More
specifically, when both T400 and T550 were equal to or more
than 85% and a ratio T400/T550 was equal to or more than 0.95,
the coloring was judged to be ".circleincircle.". When at least one of
T400 and T550 was equal to or more than 80% and less than 85%,
and the ratio T400/T550 was equal to or more than 0.95, the
coloring was judged to be "◯". On the other hand, when at
least one of T400 and T550 was less than 80%, or when the ratio
T400/T550 was less than 0.95, the coloring was judged to be
"X". When the judgment was "◯" and ".circleincircle.", it was
evaluated that there was no coloring.

[0087]The coefficient of thermal expansion (α30/380) in a range
of 30° C. to 380° C. inclusive was calculated by
manufacturing a cylindrical glass sample whose diameter and length were
5.0 mm and 12 mm respectively, and measuring a difference between the
coefficient of thermal expansion of the cylindrical glass sample and the
coefficient of thermal expansion of a standard quartz glass sample whose
coefficient of thermal expansion was evaluated.

[0088]As for the evaluation of the glass devitrification, a glass sample
which was crushed so as to have a particle diameter of about 2 mm was put
in a temperature gradient furnace which was set to be in a range of
500° C. to 1000° C. inclusive, and the glass sample was
taken out from the temperature gradient furnace after being left for four
hours to observe a crystal. When a temperature range in which the crystal
was precipitated was in a range of 700° C. to 800° C.
inclusive, the glass devitrification was judged to be "◯".
When the temperature range was lower than 700° C. or higher than
800° C., the glass devitrification was judged to be "X".

[0089]Each of conventional examples 1 and 2 is glass having the same
composition as the conventional glass, and has the ultra violet shielding
effect. However, the devitrification is high because the glass contains
TiO2, thereby the glass is not suitable for a lamp.

[0090]Each of embodiments 1 to 5 is the glass of the present invention.
Regarding the glass of each of the embodiments 1 to 5, the content of
MoO3 satisfies the constituents of the glass composition of the
present invention, the ultra violet shielding effect is high, and
coloring is less likely to occur. Above all, the glass of each of the
embodiments 3 to 5 sufficiently shields even a 313 nm ultra violet ray.
Therefore, the glass is suitable for a lamp for a backlight of a display
device such as a liquid crystal display device.

[0091]Note that regarding the glass of each of the embodiments 2 and 3, an
additive amount of an oxidant is less than 0.5 times as large as
MoO3, which is insufficient. As a result, the visible light
transmittance is lower compared with the glass of each of the embodiments
1, 4, and 5.

[0092]As for the glass of a comparative example 1, since the content of
MoO3 is too low, a transmittance of a 254 nm ultra violet ray is
high. Therefore, the ultra violet shielding effect is insufficient,
thereby the glass is not suitable for a lamp.

[0093]As for the glass of comparative example 2, since the content of
MoO3 is too high, a transmittance of visible light is low.
Therefore, the glass is colored and is not suitable for a lamp.

INDUSTRIAL APPLICABILITY

[0094]The glass composition for lamps of the present invention can be used
in the wide range of all types of lamps. The glass composition for lamps
of the present invention is particularly suitable for a cold cathode
fluorescent lamp and the like of a backlight for a liquid crystal display
device that requires high-quality displays, such as liquid crystal
display TVs, displays for PCs, liquid crystal panels for cars and the
like.